The present invention relates to methods of manufacturing printheads as employed in electrostatic printers, and the like, and, more particularly, to the method of manufacturing an electrostatic printhead or the like of the present invention comprising the steps of, forming a pattern of parallel, spaced, first printwire traces and connective conductors on one side of an insulative substrate (primarily epoxy glass or equivalent) with ends of the first printwire traces terminating in a common plane defining a printface of the printhead; adding additional conductive material to the first printwire traces adjacent the common plane to give them a substantially square cross-section; forming a pattern of parallel, spaced, second printwire traces and connective conductors on a second side of the insulative substrate with ends of the second printwire traces terminating in the common plane defining the printface of the printhead; and, adding additional conductive material to the second printwire traces adjacent the common plane to give them a substantially square cross-section. Even more specifically, it relates to the above method and additionally comprising the steps of, applying a first insulating layer over a portion of the first connective conductors with first vias in the first insulating layer positioned on the first connective conductors where electrical connection is to be made thereto; forming a plurality of first conductive busses on the insulating layer and crossing the first connective conductors and the first vias including causing a conductive material to be formed in the first vias between the first connective conductors and the first conductive busses to cause electrical connection therebetween; applying a second insulating layer over a portion of the second connective conductors with second vias in the second insulating layer positioned on the second connective conductors where electrical connection is to be made thereto; and, forming a plurality of second conductive busses on the insulating layer and crossing the second connective conductors and the second vias including causing a conductive material to be formed in the second vias between the second connective conductors and the second conductive busses to cause electical connection therebetween.
Electrostatic printheads, and the like, as manufactured by prior art techniques tend to be very expensive because of the labor intensive nature of the process. In this regard, for a more detailed discussion of the prior art in the manufacture of such printheads, attention is directed to U.S. Pat. No. 4766448 entitled Electrostatic Printhead Method and Apparatus by James Hack et al. and co-pending application Ser. No. 170,439, filed 21 Mar. 1988 by David T. Beegan entitled Electrostatic Printhead and Method of Manufacture, both of which are owned by the common assignee of this application.
A typical electrostatic printhead comprises two closely spaced rows of wires which are penpendicular to the printing face of the printhead where they terminate. The wires of one row are offset half the distance between the wires in the adjacent row. This results in much closer spacing between adjacent print positions than would be possible with all the wires on one row. The closer the spacing, of course, the better the quality of the printed material that is produced. Each typical printhead contains literally tens of thousands of wires.
Most printheads to date have been produced by hand wiring techniques. As depicted in FIG. 1, wire 10 is wound around a cylindrical mandrel 12. The printhead body 14 is formed by molding a resin material, or the like, about the wires 10 in a slot 16 provided in the mandrel for the purpose. As depicted in FIG. 1, the wires 10 are then cut along one face of the printhead body 14. That face becomes the printing face. The wires 10 extend from the other or back face. As depicted in FIG. 2, the most common assembly technique to date is to have the wires 10 hand soldered to the conductors 18 on a printed circuit board 20. Because of the labor intensive nature of such a process, it has been accomplished as a "cottage industry" in locations where labor is less costly in order to keep the cost of manufacture within reasonable limits.
As the requirements for electrostatic printheads have increased, the ability to meet the needs in a cottage industry environment has not kept pace with the demand. Accordingly, there has been considerable interest in developing a method of manufacture which eliminates the hand soldering step and replaces it with a reliable, mechanized alternative. One approach as disclosed in the above-referenced Hack et al. patent is as shown in FIGS. 3 and 4. In that approach, the printhead body 14 is formed according to the technique of FIG. 1. The wires 10, however, are cut from both faces. The exposed ends of the wires 10 on the back face of the printhead body 14 are then joined to the conductors 18 of a pair of printed circuit boards 20 by wire bonding wires 22. The printed circuit boards 20 are then folded towards one another and bonded to the printhead body 14 with a "potting" material 24, or the like, to form a unitary printhead 26 as depicted in FIG. 4.
The approach of the above-referenced Beegan application is depicted in FIGS. 5-7. As shown in FIG. 5, the conductors 18 of two printed circuit boards 20 placed close adjacent one another with the conductors 18 in end-to-end relationship are joined by wire bonding wires 22 bonded to the conductors 18 as represented by the arrows. The wires 22 are then cut in half as indicated in FIG. 6 to form two half printhead elements 28. As depicted in FIG. 7, the two half printhead elements 28 are then positioned in parallel to one another with the cut ends of the wires 22 in proper alignment to form the print wires and then assembly joined together with potting material 24, or the like, as before, to form a unitary printhead 26 as depicted in FIG. 7.
While both these techniques will work for their intended purpose, the wire bonding equipment to do the specific task does not exist. Likewise, there is no presently available equipment capable of placing, bonding, and cutting the wires 22 as shown in FIG. 6 without bending the wires out of perfect alignment. Because of the size of the wires, spacing, etc. required to produce an acceptable electrostatic printhead, this is a critical limitation to emloying the technique at a commercial level in the near future.
What is needed is a method of manufacturing electrostatic printheads, and the like, which is completely mechanical in nature like the prior art methods of FIGS. 3-7 above; but, which employs assembly apparatus and techniques presently available in the art for manufacture on a commercial basis.
Wherefore, it is the object of the present invention to provide such an immediately implementable method for manufacturing electrostatic printheads according to fully mechanized techniques.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.